When providing players with inherent bonuses (they count as having +1 weapons, neck slot, and armor from levels 2-5 ,+2 from 6-10, and so on.) how often should players receive actual magic items, and how often should they receive magic boons?

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Trying the -2 parcels out seems to fight strongly with a small player count, as the number of parcels (or random parcel generation) already severely reduces the number of item drops. Does the reduced treasure system break down for low player counts?

That's a tough question to answer in a direct way. In most of the games I've seen it's an either/or situation. You either have a low magic world (i.e. Dark Sun) and characters receive inherent bonus and might see a single magic item in their entire life, or maybe none at all. Or, you have a regular to high magic world where characters receive a few magic items per tier but would not get any inherent bonuses.

It comes down to flavor and what kind of feel to you want magic items to have. Are magic items pretty common and can be bought at the local magic sword shop, or are they so rare that many people in the world have never even see a magically enchanted item. Or anything in between those two extremes. Ask your players what level of magic they would like to see and adjust accordingly.